[228 



HANDBOOK OF PHYSIOLOGY 



NEUROPHYSIOLOGY II 



induce still further improved performance, indicating 

 a species difiference {35). 



As compared with the slow gradual loss of sex 

 behavior in male animals on castration, the loss of 

 receptivity and estrous cycles on ovariectomy in fe- 

 males is immediate and practically complete. Of the 

 common laboratory animals only the female rabbit 

 will occasionally remain receptive after castration 

 (45). The wide variety of female copulatory behavior 

 patterns in the common domestic and laboratory 

 species has been described by Young (97). Typically, 

 the female depresses her back and raises her pelvis in 

 a lordosis response and, after intromission, remains 

 quiescent as in the rabbit or undergoes a more or less 

 violent rolling, rubbing, squirming after-reaction as 

 seen in the cat. 



Many ovariectomized forms, including the dog, cat 

 and rabbit, can be restored to a state of practically 

 complete estrus with estrogen alone. Even in these 

 forms the degree of heat may be temporarily elevated 

 still further with progesterone. Rats, mice, guinea pigs 

 and hamsters ordinarily require progesterone follow- 

 ing estrogen priming to induce a recepti\'e state (21). 

 In the hamster the combination is needed to subdue 

 the female's aggressiveness as well as to promote 

 estrus (53). The period of estrus induced by the 

 combination of steroids is limited to a few hours after 

 which the animal is decidedly nonreceptive and, in 

 the case of the hamster, very aggressive. This anestrous 

 phase following progestrone treatment has been em- 

 phasized to the extent that some authors have disre- 

 garded the earlier estrous phase. 



Among the lower forms such as the rat, guinea pig 

 and rabbit, each sex has the inherent capacity for 

 performing the copulatory pattern of the opposite 

 .sex (10, 35, 97). The female rat may show mounting 

 behavior at any time during the estrus cycle or even 

 after ovariectomy, whereas the female guinea pig and 

 rabbit reveal male behavior only at the height of 

 natural or estrogen-progesterone induced heat. Simi- 

 larly, a male rat on an o\erdosage of testosterone 

 may show the female pattern. With threshold hor- 

 monal complements, intrinsic or exogenous, each sex 

 appears to prefer its own behavior pattern; with 

 superthreshold levels it is prone to perform the pattern 

 of the opposite sex, especialK in the presence of indi- 

 viduals of its own sex. 



Further evidence of the nonspecificity of sex hor- 

 mones comes from experiments in which castrate fe- 

 males have been treated with testosterone and castrate 

 males with estrogen. Whereas in the prepuberal state 

 each hormone does tend to induce tlie iiehavior char- 



acteristic of its sex regardless of whether the recipient 

 is male or female, adult castrates usually regain their 

 sex-specific behavior pattern whether treated with 

 estrogen or testosterone (10, 41 ). In the ovariectomized 

 rabbit Klein (55) reports that testosterone pellets 

 maintain a highly estrous condition indefinitely. Such 

 treatment leads to an aggressive attitude towards 

 other females (Kawakami & Sawyer, unpublished 

 observations), thus differing from natural or estrogen- 

 induced heat. 



Complete mating behavior patterns do not ap- 

 pear to be innate in any of the common laboratory 

 species with the po.ssible exception of the rat (98). 

 Guinea pigs, dogs, monkeys and chimpanzees reared 

 in isolation all showed some deficiency in mating as 

 compared with controls of equal age brought up in 

 association with other members of the same species. 



Male animals of many species adopt a territory in 

 which they will mate readily and out of which they 

 show extreme reluctance to copulate. In the labora- 

 tory this is especially true of cats (41) of which more 

 will be discussed below. 



Beach (13) has recently proposed that mating be- 

 havior in the male rat consists of two principal 

 processes: an arousal mechanism, and an intromission 

 and ejaculatory mechanism. Electrocon\ulsive shock 

 inhibits the arousal mechanism but facilitates the 

 ejaculatory process (35). 



The hormonal requirements or accompaniments of 

 maternal behavior have been studied extensively in 

 rats (II, 96). Such activities as nest building, retriev- 

 ing and cuddling newborn young are dominant during 

 late pregnancy and lactation. Rats at this stage may 

 'mother' an adult mouse (49). Estrogen appears to 

 inhibit maternal responses (44) even in dosages too 

 small to interrupt lactation (95). Anterior pituitary 

 extracts were found to induce adult virgin rats to re- 

 trieve newborn young (96). Riddle et al. (74) showed 

 that an appropriately timed injection of prolactin 

 would evoke maternal liehavioral activities in a 

 high percentage of their \irgin female rats. 



NEUR.\L MECHANISMS .^iND CENTERS AS REVEALED 

 BY LESION EXPERIMENTS 



As in other types of behavior patterns, rcproducii\c 

 behavior involves afferent, central and effector mecha- 

 nisms. Various components of the patterns of the two 

 sexes have been ascribed to different functional levels 

 within the central nervous system, and considerable 

 research has been aimed at locating; the sites of 'sex 



